The copper-containing amine oxidases (CAOs) are a diverse family of enzymes which catalyze the oxidative deamination of primary amines. In mammals, classes of CAOs have been directly linked with chronic diabetic disorders and heart failure, making them a target for pharmaceutical investigation. CAOs are produced in an initially immature, inactive form. To become functional, a tyrosine sidechain from a specific active site residue must be converted into a redox-active cofactor, 2,4,5-trihydroxyphenylalaninequinone (TPQ). The process of cofactor maturation (referred to as biogenesis) occurs by a self-processing mechanism within the enzyme, and is relatively unexplored. This proposal details four sets of experiments aimed at understanding the TPQ biogenesis mechanism in a CAO from yeast (Hansenula polymorpha). Specifically, the goals are: (1) to characterize an intermediate in biogenesis; (2) to probe the electronic character of the active site Cu(II); (3) to elucidate a site of dioxygen binding; (4) to define roles of active site residues in biogenesis.